Conventionally, as a backup function provided in a storage system, a copy function of creating mirrors of logical volumes in the same storage system without passing through the host (hereinafter referred to as the “in-storage copy function”) exists.
Meanwhile, as another backup function installed in the storage system, a copy function of creating mirrors of logical volumes between two storage systems (hereinafter referred to as the “remote copy function”) is also well known.
As methods for remote copy using the remote copy function, the synchronous method by which remote copy to logical volumes as the backup destination is performed for the relevant data in synchronization with the data written to the logical volumes and the asynchronous method by which remote copy to logical volumes as the backup destination is performed for data asynchronously with the data written to the logical volumes as the backup target exist.
By the synchronous method, after the data written to the logical volumes is copied to the logical volumes as the backup destination, a remote copy completion report is sent to the host. Therefore, the synchronous method has a problem in that, though backup is highly reliable, if the distance between the two storage systems is great, remote copy takes a fair amount of time, which deteriorates the copy efficiency.
Meanwhile, the asynchronous method issues the remote copy completion report to the host when the data has been written to the logical volumes, and then remote copy is performed for the relevant data at the convenience of the storage systems of the copy source and the copy destination. Therefore, the asynchronous method has a problem in that, though copy can be performed efficiently even if the distance between the two storage systems is great, backup has lower reliability.